Downhole rock scratcher and method for identifying strength of subsurface intervals

Abstract

Disclosed are a tool and method for identifying the relative strength of subsurface intervals through which a borehole has been drilled. The tool includes a tool body capable of being moved through a borehole. The tool body has pads mounted on movable arms. Preferably the arms can be loaded independently. Each pad carries scratchers, which are pushed against the borehole wall so as to create either deep narrow or shallow wide scratches. Preferably, the scratchers comprise either a single or dual element polycrystalline compact (PDC) cutter or suitable hard, wear resistant material such as tungsten carbide or natural diamond, and are pushed against the borehole wall by resiliently loaded arms. The depth of narrow scratches is measured, for example, by two tandem powered calipers and the width of wide scratches is visualized by a borehole imager.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to U.S. provisional application No. 60 / 899,879, filed Feb. 7, 2007, the entire disclosure of which is hereby incorporated by reference.FIELD OF THE INVENTION[0002]The present invention relates to a tool and method for identifying the relative strength of subsurface intervals, typically underground formations traversed by a borehole such as a hydrocarbon well. The present invention may be employed advantageously for detecting and characterizing weak formations.BACKGROUND OF THE INVENTION[0003]When drilling a borehole, such as a hydrocarbon well, it is necessary to obtain information of the formations being drilled. While some information can be derived from the drilled materials returned to the surface, it is often necessary that measurements be made in-situ or on larger samples in order to obtain the necessary information. Certain properties can be measured by lowering a tool into the well and making non-i...

AI Technical Summary

Problems solved by technology

However, wireline logging and logging / measurement-while-drilling may not be able to identify weak subsurface intervals that are inter-bedded within competent formations, since the logging is typically conducted overbalance, which may mask the logging measurements of weak intervals.

This approach, however, is expensive and time-consuming.

Further, it does not allow a continuous logging approach in which measurements are made continuously as the tool is moved along the borehole.

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